1. Field of the Invention
The invention relates to a communication system comprising a sending apparatus and a receiving apparatus communicating via a wireless communication medium;
said receiving apparatus comprising message receiving means for receiving via said wireless communication medium a message destined for said receiving apparatus;
said sending apparatus comprising message sending means for transmitting a message via said wireless communication medium.
The invention further relates to an end apparatus, a central apparatus, and a relay apparatus suitable for use in such a system.
2. Related Art
Communication between two apparatuses can occur in many ways. Wireless communication is widely used for communication involving portable apparatuses. For consumer electronics products, infrared light is commonly used as a carrier for wireless Communication. In known infrared communication systems, a sending apparatus, such as a hand-held remote control, comprises an infrared transmitter and a receiving apparatus, such as a television set, comprises an infrared receiver. The information is transmitted in the form of message frames. The message frames are limited to a maximum size, allowing the transmitting and receiving apparatus to use buffers with a corresponding maximum size for temporarily storing the message frames. By using simple communication protocols and operating at low bit-rates, cost-effective communication is achieved. Typically, the protocols are executed by the main CPU, requiring no dedicated logic or communication ICs in addition to an infrared transmitter or an infrared receiver. A transmission via infrared, however, can easily be disrupted, for instance, by other infrared transmitters operating at the same frequency. In order to increase reliability of such communication systems, acknowledgement mechanisms are used to report correct reception of a transmitted frame. If no acknowledgement frame is received in response to transmitting a message frame, the message frame may be retransmitted up to a predetermined maximum number of times. The acknowledgement mechanism can also be used to detect that no communication was possible, for instance, in situations where the maximum operating distance is exceeded or optical contact is broken. To support the acknowledgement mechanism, both apparatuses comprise an infrared transmitter and an infrared receiver. Such a system is known from DE-A-3508562.
This system describes the communication between two apparatuses, with the sending apparatus generating message frames and receiving acknowledgement frames, whereas the receiving apparatus receives message frames and generates acknowledgement frames in response.